Laminin, a major glycoprotein of basement membranes, exhibits saturable binding to the surface of certain neoplastic and normal cells. Examination of various cell types (i.e. human pancreatic carcinoma, melanoma and bladder carcinoma) via live cell binding techniques indicate the number of receptors to be 50-110,000 per cell depending on cell type. In our laboratory, the laminin re- ceptor has been isolated from human breast carcinoma cells and tissue and mouse melanoma cells. The receptor and subsequent ligand binding have been implicated to play an important role in tumor cell attachment, one of the steps in tumor invasion and metastasis. The proposed study is designed to measure and corre- late laminin receptor binding capacity of breast tissues with clinical information. Laminin receptor binding capacity markedly differs between benign, malignant and normal human breast tissue. Preliminary studies indicate a 50-fold increase in specific laminin binding activity in malignant versus benign breast tissues. These findings suggest a site for possible intervention in the sequence of tumor invasion.